You can do this manually, and there's a number of performance techniques based on this general principle. I've covered this before in my 'Dopplator' effect, but that was based on a rounded pulse as the LFO waveform, and didn't have any panning facilities. 'Missing Echo' is much more in the mainstream sequence of my effects, and so has dual syncable independent LFOs for panning, plus a Limiter to keep things under control if you require it, and dual syncable independent delay lines, as well as dual syncable independent LFOs to modulate the feedback. Yes, this is a lot of LFOs, but those always were the modules I ran out of first when I used to play with modular synths...

The LFO modulates the feedback in a slightly different way to the way that you might expect, and I'm still exploring things to find the optimum method. The current version first sweeps from zero feedback to the modulation setting for in-channel feedback and then back, and then sweeps from zero feedback to the modulation setting for the other-channel and then back to zero. So you get one half cycle of ordinary echo, followed by one half cycle of ping-pong echo, with all of the stereo imaging that you would expect from this arrangement. Add in the stereo auto-panning, and there's a lot that can be going on in that stereo image - if you want! As I said, I'm still trying to find the best way of controlling this, and a later version may add more facilities...

Because I have several different variations on the Echo effect available (from www.maxforlive.com) then I'm going to be adding a special easy selection page soon, so that it is easier to browse through the different variants on the echo effect that I have produced.